IAG-IASPEI 2017

講演情報

Oral

IASPEI Symposia » S06. Advancement in methodologies for CTBT monitoring

[S06-1] Advancement in methodologies for CTBT monitoring

2017年8月2日(水) 16:30 〜 18:00 Room 401 (Kobe International Conference Center 4F, Room 401)

Chairs: Tormod Kvaerna (NORSAR) , Michelle Grobbelaar (Council for Geoscience)

17:45 〜 18:00

[S06-1-06] Source array analysis for accurate relative event location at the North Korea nuclear test site

Steven Gibbons, Tormod Kvaerna, Sven Peter Naesholm, Svein Mykkeltveit (NORSAR, Kjeller, Norway)

Between October 2006 and September 2016, 5 declared underground nuclear explosions carried out at the Punggye-ri test-site in North Korea were detected both at regional and teleseismic distances. Double-difference relative location estimates are quite network-sensitive with inter-event distance estimates from regional Pn phases consistently longer than estimates from teleseismic P-phases. The seismic wavefield leaving the test-site is more complicated than predicted by a 1D velocity model. Slowness corrections for each of the rays leaving the source region can be found which reduce the double-difference time residuals and provide relative location estimates which are consistent for all seismic measurements. Source-array analysis provides a different approach to modelling the seismic wavefield leaving the DPRK test-site and supports the hypothesis that the slownesses for regional Pn waves are frequently underestimated. Given the number of events now recorded at the test-site, source-array analysis provides an important tool for analyzing subsequent events which may be problematic for classical double-difference methods. One such scenario is a low magnitude event recorded only regionally, with limitations in azimuthal coverage. Another is a test in a different part of the site for which the waveform similarity is significantly diminished at some stations.